A femto base station is basically a low cost and low power base station (BS) transceiver which is installed indoors (e.g., in a home or office) and connected to the Internet via cable, DSL, on-premise fiber optic link, or a similar IP backhaul technology. This connection is used to integrate the femto base station with the WAN wireless operator's core network.
A femto base station serves a geographic area known as a femto cell over a single carrier or channel. A femto cell typically covers a smaller geographic area or subscriber constituency than a conventional macro cell. For, example, femto base stations typically provide radio coverage in geographical areas such as one or more buildings or homes, whereas conventional macro base stations provide radio coverage in larger areas such as an entire cities or towns. The function of femto cells is similar to that of a Wireless LAN (Local Area Network). It provides the operators a low cost solution for coverage extension and for offloading users from the cellular network.
In a wireless network including femto cells, for example, upon entering a cell (femto, macro, etc.), a mobile station in an idle state receives broadcast overhead messages such as a sector-parameters message on the well-known broadcast control channel. In the current 3GPP2 CDMA2000 EVDO standards, (e.g., “cdma2000 High Rate Packet Data Air Interface Specification,” 3GPP2 C.S0024-B, Ver. 2.0 (March 2007)), broadcast sector-parameters include trigger codes.
Conventionally, a trigger code is transmitted to the mobile station by a serving base station. The mobile station uses the trigger code to identify a configuration of the serving base station. For example, a trigger code indicates to the mobile station which communication standard version (e.g., Revision 0, Revision A, etc. of the EVDO standard) is being used by the system covering a certain area. That is, the system including the serving base station.
In the idle mode, the mobile station periodically monitors (“wakes up” and receives) the broadcast control channel for changes in received sector-parameters such as the trigger code. Each time a mobile station crosses into a new cell and receives a new trigger code, the new trigger code triggers re-registration of the mobile station. That is, for example, a new trigger code causes the mobile station to send a registration message to the radio access network (RAN). If necessary, the mobile station adapts to the different standard versions of the newly entered cell in response to the new trigger code. The mobile station adapts to the different standard versions by negotiating a new set of configuration parameters (new personality). Conventionally, however, trigger codes are not used to identify an area in which to page a mobile station (hereinafter a paging area) in response to an incoming call. Instead, conventional radius-based idle registration is used.
In conventional radius-based idle registration, the mobile station calculates the distance between itself and the current serving base station and itself and the base station to which the mobile station has most recently registered (previous serving base station). If a distance between the mobile and the previous serving base station is less than a given threshold distance, the mobile does not send location update registration.
If a distance between the mobile and the previous serving base station is greater than the given threshold, the mobile sends location update registration. Location update registration is well-known in the art, and thus, a detailed discussion will be omitted for the sake of brevity.
If the mobile station does not send the location update registration, the RAN determines that the mobile is located within a given radial distance (or radial coverage area) from the previous serving base station.
After determining the appropriate paging area, the RAN pages the mobile station. Paging is used to locate the mobile station within a cell so that the RAN may route the incoming call. When paging the mobile station, the RAN pages all cells within the determined paging area. Because femto cells are usually quite small, however, a femto subnet or femto space may include, for example, hundreds of femto cells. Consequently, using radius-based idle registration, paging of a mobile station in a femto cell environment may require paging hundreds of femto cells. This may result in unnecessary traffic.
Further, as is well-known, femto cell coverage may be irregularly shaped. Consequently, at certain locations there may be a relatively large number of femto cells within a given radial coverage area, whereas at other locations there may be relatively few femto cells within a paging area. Moreover, radius based paging zones are determined by grouping cells covering the same area within a given radius. As a result, the number of the cells in a paging zone may vary substantially depending on the shape and the density of different coverage areas.
Further still, in the above-described current EVDO standards, only two-dimensional location information is broadcast by each base station. Thus, using radius based-idle registration in a femto subnet or femto space in which the femto cellular coverage is vertically deployed may also produce unnecessary paging traffic.